1. Field of the Invention
This invention relates to the field of semiconductor manufacturing processes. In particular, the present invention relates to methods and devices to enhance the reduction of organic residues over metals surfaces.
2. Description of the Related Art
Metal layers, in integrated circuits, carry signals and power from one area of the circuit to another. To form a metal structure in an integrated circuit, a metal layer may be deposited on the surface of the wafer, followed by a layer of photoresist material. The photoresist is used to coat and photosensitize the underlying surface. After deposition, the photoresist is patterned to cause the non-imaged areas of the underlying layer to resist subsequent modifications, such as etching or metal evaporation. When the etching step, for example, is finished, the photoresist is removed.
FIG. 1 is a flowchart outlining steps to remove photoresist material from a metal layer after an etching step. As shown therein, step S0 is a metal etch step in which the metal layer exposed by the photoresist is etched, to form the desired metal structures, such as conductor lines, contact pads, buses etc. After the etching step S0, the wafer is subjected to a plasma etch removal of the photoresist, as shown in step S1.
The plasma etch step S1 of FIG. 1 may be further broken down into four steps, in which the oxygen (xe2x80x9cO2xe2x80x9d), water (xe2x80x9cH2Oxe2x80x9d) vapor, and pressure remain constant while the Radio Frequency (xe2x80x9cRFxe2x80x9d) power within the plasma etch chamber and the position of the chuck or pedestal supporting the wafer within the plasma etch chamber varies from a lower position to an upper position. Table 1 outlines a process for plasma etching the photoresist and quantifies the aforementioned parameters.
As shown in Table 1, the O2 to H2O mixture of step S1 of FIG. 1 is maintained at a 5:3 ratio (300 standard cubic centimeters per minute (xe2x80x9csccmxe2x80x9d) H2O: 180 sccm O2 at a pressure of 1200 milliTorr during all four steps. In a first step, lasting 30 seconds, the chuck is maintained at a lower position, further away from the plasma source, and the RF power is turned off. In a second step, lasting only 3 seconds, the same conditions prevail and the chuck is moved to an upper position, relatively closer to the source of plasma than the lower position thereof. In a third step, the same chuck position and O2:H2O ratio are maintained and the RF power is turned on to 1200 watts for 45 seconds. The same parameters are then maintained in a fourth step, lasting 15 seconds.
In step S2 of FIG. 1, the metal layer, now etched, is then inspected to determine whether the photoresist has been properly removed from the surface of the metal layer. The photoresist is then subjected to a solvent strip to remove residual photoresist particulates from the metal layer as shown in step S3. The solvent strip of step S3 is then followed by a dry strip step S4, in an effort to remove any last remaining particulates or residual photoresist left after the solvent strip step shown at S3 in FIG. 1. After the dry strip of step S4, the metal surfaces are again inspected, as shown at step S5, to determine the efficacy of the preceding steps in removing the photoresist from the metal layer.
Despite these steps, however, some residual photoresist particulates may still be present on the metal layer, which particulates can lead to device failures and decrease the overall effective yield of the process. Such remaining photoresist particulates are schematically shown in FIG. 2. FIG. 2 shows a metal layer 100 comprising a wide area 110 and relatively narrower areas 130. For example, the wide area 110 of the metal layer 100 may be, for example, a power bus, a contact pad or some other wide metallic structure, whereas the relatively narrower areas 130, for example, represents thin conductor lines or some other narrow metal structure within an integrated circuit. It has been found that photoresist particulates, such as shown at reference numeral 120 in FIG. 2, tend to remain adhered to the wide area 110 of the metal layer 100, even after the etch and cleaning steps of FIG. 1. Indeed, while the steps shown in FIG. 1 are generally effective in removing the photoresist material from the relatively narrower areas 130 of metal layers, such as metal layer 100 of FIG. 2, the cleaning steps of FIG. 1 are somewhat less effective in removing residual photoresist over wide metal areas, such as shown at 110 in FIG. 2. Such residual photoresist on wide metal surfaces leads to increased defect count per wafer and decreases the yield of the process.
What are needed, therefore, are methods and devices to enhance the reduction of organic material residues (such as photoresist residues) over metal surfaces. In particular, what are needed are methods and devices to enhance the reduction of photoresist and other organic residues over wide metal surfaces.
An object of the present invention, therefore, is to provide methods and devices to enhance the reduction of photoresist and other organic residues over wide metal surfaces.
In accordance with the above-described objects and those that will be mentioned and will become apparent below, a method of removing organic residue from a metal surface, according to an embodiment of the present invention, comprises the steps of:
etching the metal surface with a plasma comprising H2O and an oxygen source (O2), where a volume, flow rate or molar ratio of H2O:O2 source exceeds 5:3; and
stripping the metal surface with a solvent to remove remaining organic residue from the metal surface.
According to other embodiments, the ratio of H2O vapor:O2 source ratio exceeds 5:2 by flow rate, such as about 5:1 by flow rate. The RF power during the plasma etching step may be about 1200 watts. The plasma is in a chamber having a pressure of about 50 to about 10,000 milliTorr and preferably includes one or more (hydro)fluorocarbons, such as CF4, CHF3, C2F6, C2H2F4 (e.g., Freon-134), c-C4F8, combinations thereof, or such other etchant gases as NF3 and/or SiF4. Preferably, the water vapor etching step of the present invention is carried out for a period of time of at least about 60 seconds. For example, the present etching step may be carried out for a period of time ranging from about 60 seconds to about 120 seconds, such as for a period of time ranging from about 70 seconds to about 90 seconds. The organic residue may include photoresist.
The present invention may also be viewed as a device to remove organic residue from a metal surface, comprising:
a plasma etching chamber;
a pedestal for supporting the substrate, the pedestal being mounted within said plasma etching chamber, and
at least one gas inlet into the plasma etching chamber for introducing at least a source of H2O vapor and source of O2 into the chamber at an H2O:O2 ratio by volume and/or flow ratio (unit volume per unit time) or moles exceeding 5:3. According to a further embodiment, the H2O:O2 vol./flow ratio is about 5:1.
The present invention is also a semiconductor device having at least one constituent metal layer processed by a method comprising the steps of:
forming first and second metal structures from the at least one constituent metal layer, the at least one constituent metal layer having a layer organic material thereon; and
etching the layer of organic material with a plasma having a ratio of H2O vapor to O2 of greater than 5:3 by volume, flow rate or moles.
According to further embodiments, the method may further comprise stripping residual organic material with a solvent after the etching step. The ratio of H2O vapor to O2 may be at least about 5:2. The organic material may include a photoresist. The metal layer may include at least one metal selected from the group consisting of Al, Cu, refractory metals, alloys, nitrides and silicides thereof The metal layer may comprise at least one member of the group consisting of Al, Cu, Ti, Ta, W, and alloys thereof.